1. Field of the Invention
The present invention relates to a webbing tension device, used in a seatbelt system for protecting an occupant in an emergency situation of such a vehicle as an automobile and giving a tensile force to an occupant restraining webbing to restrain the occupant in an emergency situation.
2. Description of the Prior Art
A seatbelt system for protecting an occupant in an emergency situation of a vehicle is so constructed that an occupant restraining webbing, one end thereof being fixed to the vehicle body and the other end thereof being retracted in layers into a webbing retractor, is worn by the occupant and the occupant is restrained by the webbing in an emergency situation.
The webbing retractor winding the webbing therein gives a predetermined tension to the webbing. However, the winding force of the webbing retractor is made weak or it is caused to disappear wholly so as not to give a feeling of constriction to the occupant, which results in that a slight gap exists between the webbing and the occupant. Accordingly, it will happen that the occupant can move the amount of the gap in the moving direction of the vehicle until the occupant is restrained reliably by the webbing after the drawing of the webbing from the webbing retractor is stopped in an emergency situation.
For this reason a webbing tension device for transmitting an elastic force of a spring such as a spiral spring to a takeup shaft of the webbing retractor to give a tensile force to the webbing, has been proposed in the prior art. In the webbing tension device, an action wheel receiving the elastic force is engaged with a pawl and the pawl is forcibly separated from the action wheel by an acceleration sensor such as a pendulum or the like in the emergency, whereby an action wheel is caused to rotate.
In such prior art webbing tension device, however, if the pendulum is used as an acceleration sensor, the driving force of the pendulum is amplified by utilizing a leverage so as to be transmitted to the pawl or the detecting signal of the acceleration sensor is amplified to be transmitted to the pawl by the magnetic force of a solenoid or the like because the driving force of the pendulum is small.